Optical device to improve image uniformity

ABSTRACT

An optical waveguide including an input-coupler, a first intermediate-component, a second intermediate-component and an output-coupler is described herein. The input-coupler couples, into the waveguide, light corresponding to an image associated with an input-pupil and directs the light toward the first intermediate-component. The first intermediate-component performs horizontal or vertical pupil expansion and redirects the light corresponding to the image toward the output-coupler. The second intermediate-component is a diffractive component located between the first-intermediate component and the output-coupler and performs pupil redistribution on a portion of the light corresponding to the image before the portion reaches the output-coupler. The output-coupler performs the other one of horizontal or vertical pupil expansion and couples, out of the waveguide, the light corresponding to the image. Related methods and systems are also described.

BACKGROUND

Various types of computing, entertainment, and/or mobile devices can beimplemented with a transparent or semi-transparent display through whicha user of a device can view the surrounding environment. Such devices,which can be referred to as see-through, mixed reality display systems,or as augmented reality (AR) systems, enable a user to see through thetransparent or semi-transparent display of a device to view thesurrounding environment, and also see images of virtual objects (e.g.,text, graphics, video, etc.) that are generated for display to appear asa part of, and/or overlaid upon, the surrounding environment. Thesedevices, which can be implemented as head-mounted display (HMD) glassesor other wearable display devices, but are not limited thereto, oftenutilize optical waveguides to replicate an image, e.g., produced by adisplay engine, to a location where a user of a device can view theimage as a virtual image in an augmented reality environment. As this isstill an emerging technology, there are certain challenges associatedwith utilizing waveguides to display images of virtual objects to auser.

SUMMARY

Certain embodiments of the present technology relate to an apparatus foruse in replicating an image associated with an input-pupil to anoutput-pupil. Embodiments of the present technology also relate to anear-eye or heads-up display system that include such an apparatus.Further embodiments of the present technology relate to methods for usewith display systems.

In accordance with certain embodiments, an apparatus includes an opticalwaveguide having an input-coupler, a first intermediate-component, asecond intermediate-component and an output-coupler. The input-couplerof the optical waveguide is configured to couple, into the opticalwaveguide, light corresponding to the image associated with aninput-pupil and configured to direct the light corresponding to theimage toward the first intermediate-component. The firstintermediate-component is configured to perform one of horizontal orvertical pupil expansion on the light corresponding to the image that isdirected toward the first intermediate-component by the input-couplerand configured to redirect the light corresponding to the image towardthe output-coupler. The second intermediate-component is a diffractivecomponent located between the first-intermediate component and theoutput-coupler and is configured to perform pupil redistribution on aportion of the light corresponding to the image before the portion ofthe light reaches the output-coupler. The output-coupler is configuredto perform the other one of horizontal or vertical pupil expansion andis configured to couple, out of the optical waveguide, the lightcorresponding to the image that has traveled through the opticalwaveguide from the input-coupler to the output-coupler at least in partby way of total internal reflection (TIR).

In accordance with certain embodiments, the secondintermediate-component diffracts and thereby interacts with the lightcorresponding to the image travelled by way of TIR from the firstintermediate-component to the output-coupler. For example, the secondintermediate-component can be configured to cause both zero-orderdiffraction and at least one of positive or negative first-orderdiffraction. The first intermediate-component can also be configured tocause both zero-order diffraction and at least one of positive ornegative first-order diffraction.

In accordance with certain embodiments, the secondintermediate-component is configured to cause the light that is outputfrom the optical waveguide by the output-coupler to have a more uniformintensity distribution compared to if the second intermediate-componentwere absent and the light corresponding to the image travelled by way ofTIR from the first intermediate-component to the output-coupler withoutinteracting with the second intermediate-component. More specifically,the second intermediate-component can be configured to increase overlapof pupils that are replicated within the waveguide compared to if thesecond intermediate-component were absent.

In certain embodiments, with respect to a front view of the waveguide,the first intermediate-component is located to a side of theinput-coupler, the second intermediate-component is located below thefirst intermediate-component and the output-coupler is located below thesecond intermediate-component. Other relative locations of the variousoptical components are also possible and within embodiments of thepresent technology.

A method according to an embodiment of the present technology includesusing a display engine to produce light corresponding to an image. Sucha method also includes using an input-coupler of the optical waveguideto couple the light corresponding to the image into the opticalwaveguide and to direct the light corresponding to the image toward afirst intermediate-component of the optical waveguide. A firstintermediate-component of the optical waveguide is used to redirect thelight corresponding to the image toward an output-coupler of the opticalwaveguide. A second intermediate-component of the optical waveguide,which is a diffractive component located between the first-intermediatecomponent and the output-coupler of the optical waveguide, is used toperform pupil redistribution on a portion of the light corresponding tothe image before the portion of the light reaches the output-coupler.The method also includes using the output-coupler of the opticalwaveguide to couple, out of the optical waveguide, the lightcorresponding to the image that has traveled through the opticalwaveguide from the input-coupler to the output-coupler at least in partby way of TIR.

In accordance with certain embodiments, the display engine that is usedto produce light corresponding to an image includes an illuminator, animage former and at least one collimating lens. The illuminator caninclude one or more light sources each of which is configured to emitnarrowband light having a full width at half maximum (FWHM) bandwidththat is less than 10 nm. The image former can be configured to producean image using the narrowband light produced by the illuminator. The atleast one collimating lens can be arranged and configured to receive andcollimate light corresponding to the image produced by the image formerand direct the light corresponding to the image toward the input-couplerof the optical waveguide.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are front, top and side views, respectively, of anexemplary waveguide that can be used to replicate an image associatedwith an input-pupil to an expanded output-pupil.

FIG. 2 is side view of the exemplary waveguide introduced with referenceto FIGS. 1A, 1B and 1C, and also shows a display engine that generatesan image including angular content that is coupled into the waveguide byan input-coupler, and also shows an eye that is viewing the image withinan eyebox that is proximate the output-coupler.

FIG. 3, which is similar to FIG. 1A because it provides a front view ofthe waveguide, is used to explain how light that is coupled into thewaveguide by an input-coupler, travels by way of total internalreflection (TIR) from the input-coupler to an intermediate-component,and by way of TIR from the intermediate-component to an output-coupler,where it exits the waveguide.

FIG. 4A is a graph of the spectral characteristics of red light emittedby an exemplary wideband red light source, such as a red light emittingdiode (LED).

FIG. 4B is a graph of the spectral characteristics of red light emittedby an exemplary narrowband red light source, such as a red laser diode(LD).

FIG. 5A, which shows a side view of an optical waveguide, illustrateshow a diffractive input-coupler of the waveguide causes wideband lightincident thereon (which may be produced by the wideband light sourcethat produces the light having the spectral characteristics shown inFIG. 4A) is dispersed into multiple wavelengths that each propagate byway of TIR at a respective different angle within the waveguide.

FIG. 5B, which shows a side view of an optical waveguide, illustrateshow a diffractive input-coupler of the waveguide causes relativelyminimal dispersion of narrowband light incident thereon (which may beproduced by the narrowband light source that produces the light havingthe spectral characteristics shown in FIG. 4B), and thus, separationinto relatively few wavelengths that each propagate by way of TIR at arespective different angle within the waveguide.

FIG. 6A conceptually illustrate how a pupil is replicated within anoptical waveguide as light produced by a wideband light source (whichmay be produced by the wideband light source that produces the lighthaving the spectral characteristics shown in FIG. 4A) travels by way ofTIR from an input-coupler to an intermediate-component, and by way ofTIR from the intermediate-component to an output-coupler, where it exitsthe waveguide.

FIG. 6B conceptually illustrate how a pupil is replicated within anoptical waveguide as light produced by a narrowband light source (whichmay be produced by the narrowband light source that produces the lighthaving the spectral characteristics shown in FIG. 4B) travels by way ofTIR from an input-coupler to an intermediate-component, and by way ofTIR from the intermediate-component to an output-coupler, where it exitsthe waveguide.

FIG. 7 is used to illustrate non-uniformities in local and globalintensities which may occur when performing imaging, and morespecifically pupil replication, using an optical waveguide.

FIG. 8A illustrates a front view of an optical waveguide according to anembodiment of the present technology. FIG. 8B is an exemplary side viewof the optical waveguide whose front view is shown in FIG. 8A.

FIG. 9 is a high level flow diagram that is used to describe methodsaccording to certain embodiments of the present technology.

FIG. 10 illustrates a front view of an optical waveguide that supports agreater field of view (FOV) than the optical waveguides of the earlierFIGS.

FIGS. 11 and 12 illustrates how the optical waveguide introduced withreference to FIG. 10 can be modified, in accordance with certainembodiments of the present technology.

DETAILED DESCRIPTION

Certain embodiments of the present technology relate to apparatuses foruse in replicating an image associated with an input-pupil to anoutput-pupil. Such apparatuses can include a waveguide. As will bediscussed in further details below, where waveguides are used to performpupil replication (also referred to as image replication),non-uniformities in local and global intensities may occur, which mayresult in dark and light fringes and dark blotches when the replicatedimage is viewed, which is undesirable. Certain embodiments describedherein can be used to improve intensity distributions, and thereby, canbe used to improve the replicated image when viewed. More generally,embodiments of the present invention can be used to improve imageuniformity.

In the description that follows, like numerals or reference designatorswill be used to refer to like parts or elements throughout. In addition,the first digit of a three digit reference number, or the first twodigits of a four digit reference number, identifies the drawing in whichthe reference number first appears.

FIGS. 1A, 1B and 1C are front, top and side views, respectively, ofexemplary optical waveguide 100 that can be used to replicate an imageassociated with an input-pupil to an expanded output-pupil. The term“input pupil,” as used herein, refers to an aperture through which lightcorresponding to an image is overlaid on an input-coupler of awaveguide. The term “output pupil,” as used herein, refers to anaperture through which light corresponding to an image exits anoutput-coupler of a waveguide. The optical waveguide 100 will often bereferred to hereafter more succinctly simply as a waveguide 100. As willbe discussed in further detail below with reference to FIG. 2, the imagethat the waveguide 100 is being used to replicate, and likely alsoexpand, can be generated using a display engine.

Referring to FIGS. 1A, 1B and 1C, the optical waveguide 100 includes abulk-substrate 106 having an input-coupler 112 and an output-coupler116. The input-coupler 112 is configured to couple light correspondingto an image associated with an input-pupil into the bulk-substrate 106of the waveguide. The output-coupler 116 is configured to couple thelight corresponding to the image associated with the input-pupil, whichtravels in the optical waveguide 100 from the input-coupler 112 to theoutput-coupler 116, out of the waveguide 100 so that the light is outputand imaged from the output-pupil.

The bulk-substrate 106, which can be made of glass or optical plastic,but is not limited thereto, includes a first major surface 108 and asecond major surface 110 opposite and parallel to the first majorsurface 108. The first major surface 108 can alternatively be referredto as the front-side major surface 108 (or more simply the front-sidesurface 108), and the second major surface 110 can alternatively bereferred to as the back-side major surface 110 (or more simply theback-side surface 110). As the term “bulk” is used herein, a substrateis considered to be “bulk” substrate where the thickness of thesubstrate (between its major surfaces) is at least ten times (i.e., 10×)the wavelength of the light for which the substrate is being used as anoptical transmission medium. For an example, where the light (for whichthe substrate is being used as an optical transmission medium) is redlight having a wavelength of 620 nm, the substrate will be considered abulk-substrate where the thickness of the substrate (between its majorsurfaces) is at least 6200 nm, i.e., at least 6.2 μm. In accordance withcertain embodiments, the bulk-substrate 106 has a thickness of at least25 μm between its major surfaces 108 and 110. In specific embodiments,the bulk-substrate 106 has a thickness (between its major surfaces)within a range of 25 μm to 1000 μm. The bulk-substrate 106, and moregenerally the waveguide 100, is transparent, meaning that it allowslight to pass through it so that a user can see through the waveguide100 and observe objects on an opposite side of the waveguide 100 thanthe user's eye(s).

The optical waveguide 100 in FIGS. 1A, 1B and 1C is also shown asincluding an intermediate-component 114, which can alternatively bereferred to as an intermediate-zone 114. Where the waveguide 100includes the intermediate-component 114, the input-coupler 112 isconfigured to couple light into the waveguide 100 (and morespecifically, into the bulk-substrate 106 of the waveguide 100) and in adirection of the intermediate-component 114. The intermediate-component114 is configured to redirect such light in a direction of theoutput-coupler 116. Further, the intermediate-component 114 isconfigured to perform one of horizontal or vertical pupil expansion, andthe output-coupler 116 is configured to perform the other one ofhorizontal or vertical pupil expansion. For example, theintermediate-component 114 can be configured to perform horizontal pupilexpansion, and the output-coupler 116 can be configured to verticalpupil expansion. Alternatively, if the intermediate-component 114 wererepositioned, e.g., to be below the input-coupler 112 and to the left ofthe output-coupler 116 shown in FIG. 1A, then the intermediate-component114 can be configured to perform vertical pupil expansion, and theoutput-coupler 116 can be configured to perform horizontal pupilexpansion. In certain embodiments, the intermediate-component isconfigured as a fold-grating. In other embodiments, theintermediate-component is a mirror based component, rather than agrating based component.

The input-coupler 112, the intermediate-component 114 and theoutput-coupler 116 can be referred to collectively herein as opticalcomponents 112, 114 and 116 of the waveguide, or more succinctly ascomponents 112, 114 and 116.

In FIG. 1A, the input-coupler 112, the intermediate-component 114 andthe output-coupler 116 are shown as having rectangular outer peripheralshapes, but can have alternative outer peripheral shapes. For example,the input-coupler 112 can alternatively have a circular outer peripheralshape, but is not limited thereto. For another example, theintermediate-component can have a triangular or hexagonal outerperipheral shape, but is not limited thereto. Further, it is noted thatthe corners of each of the peripheral shapes, e.g., where generallyrectangular or triangular, can be chamfered or rounded, but are notlimited thereto. These are just a few exemplary outer peripheral shapesfor the input-coupler 112, the intermediate-component 114 and theoutput-coupler 116, which are not intended to be all encompassing.

As can best be appreciated from FIGS. 1B and 1C, the input-coupler 112,the intermediate-component 114 and the output-coupler 116 are all shownas being provided in or on a same surface (i.e., the back-side surface110) of the waveguide 100. In such a case, the input-coupler 112 can betransmissive (e.g., a transmission grating), the intermediate-component114 can be reflective (e.g., a reflective grating), and theoutput-coupler 116 can also be reflective (e.g., a further reflectivegrating). The input-coupler 112, the intermediate-component 114 and theoutput-coupler 116 can alternatively all be provided in the front-sidesurface 110 of the waveguide 100. In such a case, the input-coupler 112can be reflective (e.g., a reflective grating), theintermediate-component 114 can be reflective (e.g., a further reflectivegrating), and the output-coupler 116 can also be transmissive (e.g., atransmission grating).

Alternatively, the input-coupler 112, the intermediate-component 114 andthe output-coupler 116 can all be embedded (also referred to asimmersed) in the bulk-substrate 106. For example, the bulk-substrate 106can be separated into two halves (that are parallel to the majorsurfaces 108 and 110), and the input-coupler 112, theintermediate-component 114 and the output-coupler 116 can be provided in(e.g., etched into) one of the inner surfaces of the two halves, and theinner surfaces of the two halves can be adhered to one another.Alternatively, the bulk-substrate 106 can be separated into two halves(that are parallel to the major surfaces 108 and 110), and theinput-coupler 112, the intermediate-component 114 and the output-coupler116 can be provided between the inner surfaces of the two halves. Otherimplementations for embedding the input-coupler 112, theintermediate-component 114 and the output-coupler 116 in thebulk-substrate 106 are also possible, and within the scope of theembodiments described herein. It is also possible that one of theinput-coupler 112, the intermediate-component 114 and the output-coupler116 is provided in or on the front-side surface 108 of the waveguide108, another one of the components 112, 114 and 116 is provided in or onthe back-side surface 110, and the last one of the components 112, 114and 116 is embedded or immersed in the bulk-substrate 106. Moregenerally, unless stated otherwise, any individual one of theinput-coupler 112, the intermediate-component 114 and the output-coupler116 can be provided in or on either one of the major surfaces 108 or 110of the bulk-substrate 106, or embedded therebetween.

The input-coupler 112, the intermediate-component 114 and theoutput-coupler 116 can each be implemented as a diffraction grating, ormore generally, as a diffractive optical element (DOE). Such DOEs can beproduced using holographic processes, in which case, the DOEs can bemore specifically referred to a holographic optical elements (HOEs). Theinput-coupler 112 can alternatively be implemented as a prism, areflective polarizer or can be mirror based. Similarly, theoutput-coupler 116 can alternatively be implemented as a prism, areflective polarizer or can be mirror based. Depending upon the specificconfiguration and implementation, any one of the input-coupler 112, theintermediate-component 114 and the output-coupler 116 can be reflective,diffractive or refractive, or a combination thereof, and can beimplemented, e.g., as a linear grating type of coupler, a holographicgrating type of coupler, a prism or another type of optical coupler. Theintermediate-component 114, as noted above, can be implemented using afold-grating, or can alternatively be implemented as a mirror basedpupil expander, but is not limited thereto.

Where the input-coupler 112, the intermediate-component 114 and theoutput-coupler 116 are implemented in or on one (or both) of thesurfaces 108 and/or 110 of the waveguide 100, one or more of them can beimplemented as a surface grating, or more specifically, as a surfacerelief grating (SRG). A surface grating is a periodic structure in or onthe surface of an optical component, such as a bulk-substrate 106. Whenthe periodic structure is due to modulation of the surface itself, or acoating on the surface, it is referred to as a surface relief grating(SRG). An exemplary SRG includes uniform straight grooves in or on asurface of an optical component that are separated by uniform straightgroove spacing regions. The nature of the diffraction by an SRG dependsboth on the wavelength of light incident on the grating and variousoptical characteristics of the SRG, such as line spacing, groove depthand groove slant angle. An SRG can be fabricated by way of a suitablemicrofabrication process, which may involve etching of and/or depositionon a substrate (e.g., the bulk-substrate 106) to fabricate a desiredperiodic microstructure in or on the substrate to form an opticalcomponent, which may then be used as a production master such as a moldor mask for manufacturing further optical components. An SRG is anexample of a Diffractive Optical Element (DOE).

Where the input-coupler 112, the intermediate-component 114 and/or theoutput-coupler 116 is an SRG, each such SRG can be etched into one ofthe major surfaces 108 or 110 of the bulk-substrate 106. In suchembodiments, the SRG can be said to be formed “in” the bulk-substrate106. Alternatively, each SRG can be physically formed in an isotropiccoating that covers one of the major surfaces 108 or 110 of thebulk-substrate 106, in which case each such SRG can be said to be formed“on” the bulk-substrate 106. Either way, the components 112, 114 and 116are considered parts of the waveguide 100. In certain embodiments wherethe SRG(s) are formed in an isotropic coating, which covers one of themajor surfaces 108 or 110 of the bulk-substrate 106, the isotropiccoating in which the SRG(s) is/are formed has a same index of refractionas the bulk-substrate 106.

Referring specifically to FIG. 1A, in an exemplary embodiment, theinput-coupler 112 can have surface gratings that extend in a vertical(y) direction, the output-coupler 116 can have surface gratings thatextend in a horizontal (x) direction, and the intermediate-component 114can have surface gratings that extend diagonal (e.g., ˜45 degrees)relative to the horizontal and vertical directions. This is just anexample. Other variations are also possible and within the scope ofembodiments of the present technology.

More generally, the input-coupler 112, the intermediate-component 114and the output-coupler 116 can have various different outer peripheralgeometries, can be provided in or on either of the major surfaces of thebulk-substrate, or can be embedded in the bulk-substrate 106, and can beimplemented using various different types of optical structures, as canbe appreciated from the above discussion, and will further beappreciated from the discussion below.

In general, light corresponding to an image, which is coupled into thewaveguide via the input-coupler 112, can travel through the waveguidefrom the input-coupler 112 to the output-coupler 114, by way of totalinternal refection (TIR). TIR is a phenomenon which occurs when apropagating light wave strikes a medium boundary (e.g., of thebulk-substrate 106) at an angle larger than the critical angle withrespect to the normal to the surface. In other words, the critical angle(θ_(c)) is the angle of incidence above which TIR occurs, which is givenby Snell's Law, as is known in the art. More specifically, Snell's lawspecifies that the critical angle (θ_(c)) is specified using thefollowing equation:

θ_(c)=sin⁻¹(n2/n1)

where

θ_(c) the critical angle for two optical mediums (e.g., thebulk-substrate 106, and air or some other medium that is adjacent to thebulk-substrate 106) that meet at a medium boundary,

n1 is the index of refraction of the optical medium in which light istraveling towards the medium boundary (e.g., the bulk-substrate 106,once the light is couple therein), and

n2 is the index of refraction of the optical medium beyond the mediumboundary (e.g., air or some other medium adjacent to the bulk-substrate106).

The concept of light traveling through the waveguide 100, from theinput-coupler 112 to the output-coupler 114, by way of TIR, can bebetter appreciated from FIG. 2, which is discussed below. Referring nowto FIG. 2, as in FIG. 1C, FIG. 2 shows a side view of the waveguide 100,but also shows a display engine 204 that generates an image includingangular content that is coupled into the waveguide by the input-coupler112. Also shown in FIG. 2, is representation of a human eye 214 that isusing the waveguide 100 to observe an image, produced using the displayengine 204, as a virtual image.

The display engine 204 can include, e.g., an image former 206, acollimating lens 208 and an illuminator 210, but is not limited thereto.The image former 206 can be implemented using a transmissive projectiontechnology where a light source is modulated by an optically activematerial, and backlit with white light. These technologies are usuallyimplemented using liquid crystal display (LCD) type displays withpowerful backlights and high optical energy densities. The illuminator210 can provide the aforementioned backlighting. The image former 206can also be implemented using a reflective technology for which externallight is reflected and modulated by an optically active material.Digital light processing (DLP), liquid crystal on silicon (LCOS) andMirasol® display technology from Qualcomm, Inc. are all examples ofreflective technologies. Alternatively, the image former 206 can beimplemented using an emissive technology where light is generated by adisplay, see for example, a PicoP™ display engine from Microvision, Inc.Another example of emissive display technology is a micro organic lightemitting diode (OLED) display. Companies such as eMagin and Microoledprovide examples of micro OLED displays. The image former 206, alone orin combination with the illuminator 210, can also be referred to as amicro display. The collimating lens 208 is arranged to receive adiverging display image from the image former 206, to collimate thedisplay image, and to direct the collimated image toward theinput-coupler 112 of the waveguide 100. In accordance with anembodiment, an entry pupil associated with the waveguide may beapproximately the same size as an exit pupil associated with the imageformer 206, e.g., 5 mm or less in some embodiments, but is not limitedthereto. While the collimating lens 208 is illustrated as a single lensin the FIGS., the display engine 204 can actually include multiplelenses, and more generally, one or more lens groups. Further, in FIG. 2,the collimating lens 208 is represented as a biconvex lens, but that isjust for illustration. The display engine 204 can include additionaland/or alternative type(s) of lens(es), including, but not limited to,one or more piano-convex, positive meniscus, negative meniscus,plano-concave, biconvex and/or biconcave type lens, just to name a few.

In FIG. 2, the display engine 204 is shown as facing the back-sidesurface 110 of the waveguide 100, and the eye 214 is shown as facing thefront-side surface 108 opposite and parallel to the back-side surface110. This provides for a periscope type of configuration in which lightenters the waveguide on one side of the waveguide 100, and exits thewaveguide at an opposite side of the waveguide 100. Alternatively, theinput-coupler 112 and the output-coupler 116 can be implemented in amanner such that the display engine 204 and the eye 214 are proximate toand face a same major surface (108 or 110).

The waveguide 100 can be incorporated into a see-through mixed realitydisplay system, but is not limited to use therewith. A separate instanceof the waveguide 100 and the display engine 204 can be provided for eachof the left and right eyes of a user. In certain embodiments, suchwaveguide(s) 100 may be positioned next to or between see-throughlenses, which may be standard lenses used in eye glasses and can be madeto any prescription (including no prescription). Where a see-throughmixed reality display system is implemented as head-mounted display(HMD) glasses including a frame, the display engine 204 can be locatedto the side of the frame so that it sits near to a user's temple.Alternatively, the display engine 204 can be located in a centralportion of the HMD glasses that rests above a nose bridge of a user.Other locations for the display engine 204 are also possible. In theseinstances, the user can also be referred to as a wearer. Where there isa separate waveguide for each of the left and right eyes of a user,there can be a separate display engine for each of the waveguides, andthus, for each of the left and right eyes of the user. One or morefurther adjacent waveguides can be used to perform eye tracking based oninfrared light that is incident on and reflected from the user's eye(s)214, as is known in the art. In certain embodiments, a separatewaveguide is provided for each separate color (e.g., red, green andblue) that is used to produce an image. In such embodiments, threewaveguides (used for separately guiding red, green and blue lightcorresponding to an image) can be stacked, back-to-back, to provide awaveguide assembly. Such a waveguide assembly, or individual waveguidesthereof, are examples of optical structures that are configured toutilize total internal reflection (TIR) to transfer light correspondingto an image from an input-pupil to an output-pupil where the image canbe viewed by a human eye. As explained above, such waveguides can alsobe used to provide pupil expansion. It is also possible that a singlewaveguide can be used to transfer light or multiple colors (e.g., two ormore of red, green and blue) corresponding to an image from aninput-pupil to an output-pupil where the image can be viewed by a humaneye.

FIG. 3, which is similar to FIG. 1A in that it provides a front view ofthe waveguide 100, will now be used to explain how light that is coupledinto the waveguide 100 by the input-coupler 112, can travel by way ofTIR from the input-coupler 112 to the intermediate-component 114, and byway of TIR from the intermediate-component 114 to the output-coupler116, where it exits the waveguide 100. More specifically, as explainedin more detail below, a combination of diffractive beam splitting andTIR within the waveguide 100 results in multiple versions of an inputbeam of light 302(X) being outwardly diffracted from the output-coupler116 in both the length and the width of the output-coupler 116 as outputbeams 306(X) in respective outward directions (that is, away from thewaveguide 100) that substantially match the respective inward direction{circumflex over (k)}_(in)(X) of the corresponding input beam 302(X).

In FIG. 3, beams external to (e.g., entering or exiting) the waveguide100 are represented using shading and dotted lines are used to representbeams within (i.e., internal to) the waveguide 100. Perspective is usedto indicate propagation in the z-direction (i.e., towards or way from auser), with widening of the beams in FIG. 3 representing propagation inthe positive z (i.e., +z) direction (that is towards the user). Thus,diverging dotted lines represent beams within the waveguide propagatingtowards the front-side major surface 108 of the waveguide 100, with thewidest parts (shown as large dotted circles) represent those beamsstriking the front-side major surface 108 of the waveguide 100, fromwhich they are totally internally reflected back towards the back-sidemajor surface 110 of the waveguide 100, which is represented by thedotted lines converging from the widest points to the narrowest points(shown as the small dotted circles) at which they are incident on theback-side major surface 110 of the waveguide 100.

Exemplary regions where a beam is incident on the intermediate-component114 and splits into two beams, one of which travels in the horizontaldirection and the other one of which travels in the vertical direction,are labeled S (for split or splitting). Exemplary regions where a beamis incident on the output-coupler 116 and exits the waveguide 100 arelabeled E (for exit or exiting).

As illustrated, the input beam 302(X) is coupled into the waveguide 100,e.g., by way of diffraction, by the input-coupler 112, and propagatesalong a width of the input-coupler by way of TIR in the horizontaldirection. This results in the beam 302(X) eventually striking theintermediate-component 114 at a left-most splitting region (S). When thebeam 302(X) is incident at the left-most splitting region (S), thatincident beam 302(X) is effectively split in two, e.g., by way ofdiffraction. This splitting creates a new version of that beam 304(X)(specifically a first-order diffraction mode beam) which is directed ina generally downwards vertical (−y) direction towards the output-coupler116, in addition to a zero-order diffraction mode beam (i.e. unaffectedby the diffractive component) that continues to propagate along thewidth of the intermediate-component 114 in the horizontal (+x)direction, just as the beam would in the absence of theintermediate-component 114 (albeit at a reduced intensity). Thus, aportion of the beam effectively continues to propagate alongsubstantially the whole width of the intermediate-component 114,striking the intermediate-component 114 at various splitting regions(S), with another new version of the beam (in the same downwarddirection) created at each splitting region (S). As shown in FIG. 3,this results in multiple versions of the beam being directed toward, andincident on, the output-coupler 116, with the multiple versions of thebeam being horizontally separated so as to collectively spansubstantially the width of the output-coupler 116.

As also shown in FIG. 3, each new version of the beam as created at asplitting region (S) may itself strike the intermediate-component 114(e.g., a fold grating) during its downward propagation. This can resultin a splitting of the new version of the beam, e.g., by way ofdiffraction, to create a further new version of that beam that isdirected in a horizontal (+x) direction (which is a first-orderdiffraction mode beam), in addition to a zero-order diffraction modebeam that continues to propagate in the downward vertical (−y)direction. This phenomenon may repeat numerous times within thewaveguide, as can be appreciated from FIG. 3. FIG. 3 is not drawn toscale, as many more reflections and splitting of beams are likely tooccur than illustrated in FIG. 3, e.g., as can be better appreciatedfrom FIG. 4.

In FIG. 3, the output-coupler 116 is shown as being located below theintermediate-component 114, and thus, the downward-propagating versionsof the beams will eventually be incident on the output-coupler 116, atwhich they are guided onto the various exit regions (E) associated withthe output-coupler 116. The output-coupler 116 is configured so thatwhen a version of the beam strikes the output-coupler, that beam isdiffracted to create a first-order diffraction mode beam directedoutwardly from the output-coupler 116, in an outward direction thatsubstantially matches the unique inward direction in which the originalbeam 302(X) corresponding to an image point X was input. Because thereare multiple versions of the beam propagating downwards thatsubstantially span the width of the output-coupler 116, multiple outputbeams 306(X) are generated across the width of the output-coupler 116(as shown in FIG. 3) to provide effective horizontal beam expansion,which can also be referred to as horizontal pupil expansion.

Moreover, the output-coupler 116 is configured so that, in addition tothe outwardly diffracted beams 306(X) being created at the various exitregions (E) from an incident beam, a zero-order diffraction mode beamcontinues to propagate downwards in the same specific direction as thatincident beam. This, in turn, strikes the output-coupler 116 at lowerportions thereof in the manner illustrated in FIG. 3, resulting in bothcontinuing zero-order and outward first-order beams. Thus, multipleoutput beams 306(X) are also generated across substantially the entireheight of the output-coupler 116 to provide effective vertical beamexpansion, which can also be referred to as vertical pupil expansion.

The output beams 306(X) are directed outwardly in outward directionsthat substantially match the unique input direction in which theoriginal beam 302(X) is inputted. In this context, substantiallymatching means that the outward direction is related to the inputdirection in a manner that enables a user's eye to focus any combinationof the output beams 306(X) to a single point on the retina, thusreconstructing the image point X from which the original beam 302(x)propagated or was otherwise emitted.

For a planar waveguide (i.e., a waveguide whose front-side and back-sidemajor surfaces lie substantially parallel to the xy-plane in theirentirety), the output beams 306(S) are substantially parallel to oneanother and propagate outwardly in an output propagation direction{circumflex over (k)}_(out)(X) that is parallel to the unique inwarddirection {circumflex over (k)}_(in)(X) in which the corresponding inputbeam 302(X) was directed to the input-coupler 112. That is, directingthe beam 302(X) corresponding to the image point X to the input-coupler112 in the inward direction {circumflex over (k)}_(in)(X) causescorresponding output beams 306(X) to be directed (e.g., diffracted)outwardly and in parallel from the output-coupler 116, each in anoutward propagation direction {circumflex over (k)}_(out)(X)={circumflexover (k)}_(in)(X) due to the configuration of the waveguide 100.

In the exemplary implementation described above, theintermediate-component 114 (e.g., a fold grating) is configured toprovide horizontal pupil expansion, also referred to as effectivehorizontal beam expansion; and the output-coupler 116 is configured toprovide vertical pupil expansion, also referred to as effective verticalbeam expansion. Alternatively, the intermediate-component 114 can berepositioned, e.g., below the input-coupler 112 and to the side of theoutput-coupler 116, and the components 112, 114 and 116 can bereconfigured such that the intermediate-component 114 is configured toprovide vertical pupil expansion, and the output-coupler 116 isconfigured to provide horizontal pupil expansion, as was noted above.

The exemplary waveguide 100 shown in and described with reference toFIGS. 1-3 is for use in an imaging system that relies on pupilreplication. In such systems, i.e., systems that rely on pupilreplication, the output pupils are preferably uniformly overlapping forall angles. When this is not the case, e.g., because pupils are spacedtoo far apart from one another, angular-dependentspatial-non-uniformities in intensity arise, which manifest themselvesas bright and dark image artifacts, which are undesirable.

Referring back to FIG. 2, the illuminator 210 can include one or morelight emitting elements, each of which can also be referred to as alight source. For example, the illuminator 210, which can also bereferred to as a light source assembly, can include red, green and/orblue light sources that are configured to respectively produce red lightwithin a corresponding red wavelength range, green light within acorresponding green wavelength range and blue light within acorresponding blue wavelength range. For a more specific example, theilluminator 210 can include wideband red, green and blue light emittingdiode (LEDs). Wideband, as the term is used herein, refers to lighthaving a full width at half maximum (FWHM) bandwidth that is greaterthan 10 nm, and is likely to have an FWHM bandwidth of at least 30 nm.

A wideband red LED can, for example, have a FWHM bandwidth from ˜605 nmto ˜645 nm, with an emission peak at ˜625 nm. The spectralcharacteristics of red light emitted by such an exemplary wideband redLED is illustrated in the graph of FIG. 4A. A wideband green LED can,for example have a FWHM bandwidth from ˜505 nm to ˜545 nm, with anemission peak at ˜525 nm. A graph of the spectral characteristics ofgreen light emitted by such a wideband green LED could resemble thegraph in FIG. 4A, but with the emission peak shifted down to ˜525 nm. Awideband blue LED can, for example, have a FWHM bandwidth from ˜435 nmto ˜475 nm, with an emission peak at ˜455 nm. A graph of the spectralcharacteristics of blue light emitted by such a wideband blue LED couldresemble the graph in FIG. 4A, but with the emission peak shifted downto ˜455 nm. These are just examples, which are not intended to belimiting.

Referring back to FIG. 2 again, the collimating lens 208 causes eachpixel of an image, produced by the image former 206, to be a collimatedpupil that is coupled into the waveguide 100 and then expanded usingpupil replication in the waveguide at each TIR. Even relatively smallpupils (e.g., on the order of 3 mm to 4 mm in diameter) can producesubstantially uniform images (as viewed by an eye 214 within an eyebox)when the illuminator 210 includes wideband light sources, such as LEDs.This is because LEDs have a relatively wide spectral bandwidth (e.g., onthe order of about 20 nm to 40 nm) and every wavelength (within therelatively wide spectral bandwidth) propagates at a different anglewithin the waveguide. More specifically, when wideband light emitted bya wideband light source is incident on a diffractive grating typeinput-coupler (e.g., 112), the diffracting grating disperses (i.e.,separates) the wideband light into multiple wavelengths that eachpropagate at a respective different angle within the waveguide, asillustrated in FIG. 5A. In other words, FIG. 5A illustrates how adiffractive input-coupler 112 causes the wideband light incident thereonto be dispersed into multiple wavelengths that each propagate by way ofTIR at a respective different angle within the waveguide 100. Adiffractive grating type intermediate-coupler (e.g., 114) and adiffractive grating type output-coupler (e.g., 116) also cause similardispersion of the wideband light.

FIG. 6A is used to conceptually illustrate how a pupil, represented bythe solid-lined circle 602, is replicated, as light produced by awideband light source (e.g., an LED) travels by way of TIR from theinput-coupler 112 to the intermediate-component 114, and by way of TIRfrom the intermediate-component 114 to the output-coupler 116, where itexits the waveguide 100. In FIG. 6A, each of the dotted-lined circlesrepresents a replication of the pupil 602, which may also be referred tosimply as a pupil. While represented as circles in FIG. 6A, each pupilis actually a collection of angles. When light exits the waveguide 100,proximate the output-coupler 116, a human eye, which has a lens in it,receives the collection of angles associated with a pupil and coverts itback to an image, e.g., the image produced by the display engine 204 inFIG. 2. Where the waveguide 100, and more specifically the components114 and/or 116 thereof is/are configured to perform pupil expansion,when an expanded pupil and is converted to an image (by the lens of ahuman eye), the resulting image is expanded relative to the originalimage (e.g., produced by the display engine 204 in FIG. 2).

In FIG. 6A, the pupils substantially evenly overlap one another, whichbeneficially results in smooth pupil filling of the eyebox (proximatethe output-coupler 116) from which a human eye 214 can view the image.The wide bandwidth of the LED type light source contributes to theoverlap of the pupils and the smooth pupil filling of the eyebox. Inother words, the use of one or more LEDs as the light source(s) of theilluminator 210 contributes to a substantially even pupil distributionbeing provided, which beneficially provides for a substantially uniformintensity distribution in the image.

While wideband LEDs are relatively inexpensive and readily available,there are certain benefits to using narrowband light sources, such asnarrowband laser diodes (LDs), instead of wideband LEDs to implement theilluminator 210. For example, narrowband LDs produce more collimated andcoherent light than wideband LEDs, can provide higher output power thanwideband LEDs, can produce linearly polarized light, and may enablebetter optimization of an overall imaging system. Narrowband, as theterm is used herein, refers to light having a FWHM bandwidth that isless than 10 nm, and is likely to have an FWHM bandwidth of less than 5nm (e.g., 2 nm or less). Additionally, certain types of displaytechnology, such as MEMs scanning display technology, require thatnarrowband light sources be used. Further, narrowband light sources canbe integrated into assemblies that typically weigh less than thoserequired for the integration of wideband LEDs, which is advantageouswhere the light sources are included in a portable device. Also, where anarrowband LD produces linearly polarized light, such light can providefor a higher coupling efficiency when a DOE or other coupler isconfigured to have a preferential polarization state.

A narrowband light source can include, e.g., a laser diode (LD), a superluminescent light emitting diode (SLED), or a quantum dot light emittingdiode (QD-LED), or some other light emitter element that emits lighthaving a FWHM bandwidth that is less than 10 nm. A graph of the spectralcharacteristics of red light emitted by an exemplary narrowband red LDis shown in FIG. 4B. A graph of the spectral characteristics of greenlight emitted by an exemplary narrowband green LD could resemble thegraph in FIG. 4B, but with the emission peak shifted down to ˜525 nm. Agraph of the spectral characteristics of blue light emitted by anexemplary narrowband blue LD could resemble the graph in FIG. 4B, butwith the emission peak shifted down to ˜455 nm. These are just examples,which are not intended to be limiting.

As noted above, the collimating lens 208 of a display engine 204 causeseach pixel of an image, produced by the image former 206, to be acollimated pupil that is coupled into the waveguide 100 and thenexpanded using pupil replication in the waveguide at each TIR. However,where the illuminator 210 is implemented using one or more LDs or othernarrowband light source(s), the pupil distribution may be much morespread out and less uniform than is the case where the illuminator 210is implemented using one or more LEDs or other wideband light source(s).The reasons for this can be appreciated from FIGS. 5B and 5C.

Referring to FIG. 5B, in contrast to when wideband light emitted by awideband light source is incident on a diffractive grating typeinput-coupler (e.g., 112), when narrowband light emitted by a narrowbandlight source is incident on a diffractive grating type input-coupler(e.g., 112), the diffracting grating only minimally disperses (i.e.,separates) the narrowband light into relative few wavelengths that eachpropagate at a respective different angle within the waveguide, asillustrated in FIG. 5B. In other words, FIG. 5B illustrates how adiffractive input-coupler 112 causes narrowband light incident thereonto be only minimally dispersed into relatively few wavelengths that eachpropagate by way of TIR at a respective different angle within thewaveguide 100. A diffractive grating type intermediate-coupler (e.g.,114) and a diffractive grating type output-coupler (e.g., 116) alsocause similar minimal dispersion of the narrowband light.

FIG. 6B is used to conceptually illustrate how a pupil, represented bythe solid-lined circle 602, is replicated, as light produced by anarrowband light source (e.g., an LD) travels by way of TIR from theinput-coupler 112 to the intermediate-component 114, and by way of TIRfrom the intermediate-component 114 to the output-coupler 116, where itexits the waveguide 100. In FIG. 6B, each of the dotted-lined circlesrepresents a replication of the pupil 602, which may also be referred tosimply as a pupil.

In FIG. 6B, the pupils are spread out and do not overlap one another,which detrimentally results in non-smooth pupil filling of the eyebox(proximate the output-coupler 116) from which a human eye 214 can viewthe image. Indeed, in FIG. 6B there are gaps between adjacent pupilsrepresented by the dotted-lined circles. The narrow bandwidth of lightemitted by an LD type light source contributes to the lack of overlap ofthe pupils and the non-smooth pupil filling of the eyebox. In otherwords, the use of one or more LDs as the light source(s) of theilluminator 210 can provide for a substantially uneven pupildistribution, which undesirably provides for a non-uniform intensitydistribution in the image.

FIG. 7 is used to generally illustrate the result of non-uniformities inlocal and global intensity which may occur when performing imaging usingan optical waveguide, wherein the non-uniformities can occur due tonon-uniform pupil distribution. More specifically, the dark and lightgenerally diagonal fringes are illustrative of non-uniformities in localintensity that occur due to the pupil distribution being non-uniform.Such non-uniformities can be seen as color non-uniformity and imagenoise to a viewer.

Embodiments of the present technology reduce and preferably remove thepupil replication problems induced by narrowband light sources, such asLDs, and more generally, induced when small pupils are being replicated.More specifically, certain embodiments of the present technology utilizea waveguide architecture where light is diffracted by an addeddiffractive grating an even or add number of times in order to achieve apupil replication that fills in the gaps between adjacent replicatedpupils described above with reference to FIG. 6B. If designedappropriately, using the grating equation, virtually any grating periodand grating orientation (i.e., grating angle) can be used since adeflection of an angle will be compensated by the next diffraction, aslong a majority of power is diffracted in the diffraction orders 0 andn, where m can be any even or odd integer. In accordance with certainembodiments, the diffraction orders are primarily limited to thezero-order, and the positive and/or negative first-order, so as tomitigate the possibility of ghost images.

In accordance with specific embodiments of the present technology, bydesigning the additional diffractive element in a proper way, part ofthe power of a pupil can be diffracted into a new direction into thediffraction order m, while keeping the rest of the power of the pupilpropagating at the original direction in the zero-diffractive order.Since the diffracted part of the pupil moves sideways, the size of thepupil is effectively increased. However, with the next diffraction thediffracted power is re-diffracted and propagated at the originaldirection. By targeting the diffracted direction to fill in the gapsbetween adjacent pupils, a uniform pupil distribution can be achievedthat mitigates dark regions that may otherwise appear in an image viewedfrom the eyebox.

An example of this approach is shown in FIG. 8A, which illustrates afront view of an optical waveguide 800. The waveguide 800 in FIG. 8A issimilar to the waveguide 100 discussed above with reference to many ofthe previously discussed FIGS. However, a comparison between, forexample, the waveguide 100 depicted in FIG. 6B and the waveguide 800depicted in FIG. 8A shows that the waveguide 800 includes an additionaloptical component 815, which will often be referred to herein as asecond intermediate-component 815. In other words, the waveguide 800 issimilar to the waveguide 100, except the waveguide 800 includes anadditional intermediate-component 815 located between theintermediate-component 114 and the output-coupler 116. When discussingFIG. 8A, the intermediate-component 114 will often be referred to as thefirst intermediate-component.

Referring to FIG. 8A, the optical waveguide 800 is shown as including aninput-coupler 112, a first intermediate-component 114, a secondintermediate-component 815 and an output-coupler 116. The input-coupler112 of the optical waveguide 800 is configured to couple, into theoptical waveguide 800 (and more specifically, the bulk substratethereof), light corresponding to an image associated with theinput-pupil (e.g., produced by the display engine 204) and configured todirect the light corresponding to the image toward the firstintermediate-component 114. The first intermediate-component 114 isconfigured to perform one of horizontal or vertical pupil expansion onthe light corresponding to the image that is directed toward the firstintermediate-component 114 by the input-coupler 112 and configured toredirect the light corresponding to the image toward the output-coupler116. The second intermediate-component 815 is a diffractive componentlocated between the first-intermediate component 114 and theoutput-coupler 116 and is configured to perform pupil redistribution ona portion of the light corresponding to the image before the portion ofthe light reaches the output-coupler 116. Unless stated otherwise, thesecond intermediate-component 815 can be provided in or on either one ofthe major surfaces of bulk-substrate of an optical waveguide, orembedded therebetween. The output-coupler 116 is configured to performthe other one of horizontal or vertical pupil expansion and configuredto couple, out of the optical waveguide 800, the light corresponding tothe image that has traveled through the optical waveguide 800 from theinput-coupler 112 to the output-coupler 116 at least in part by way ofTIR.

The second intermediate-component 815 diffracts and thereby interactswith the light corresponding to the image travelled by way of TIR fromthe first intermediate-component 114 to the output-coupler 116. Inaccordance with specific embodiments, the first intermediate-component114 is a diffractive optical element (DOE) configured to cause bothzero-order diffraction and at least one of positive or negativefirst-order diffraction, as can be appreciated from the discussion ofFIG. 3 above. Similarly, the second intermediate-component 815 is a DOEconfigured to cause both zero-order diffraction and at least one ofpositive or negative first-order diffraction. However, in accordancewith certain embodiments of the present technology, the angle ofdiffraction associated with the first-order diffractions caused by thesecond intermediate-component 815 will differ from the angle ofdiffraction associated with the first-order diffractions caused by thefirst intermediate-component 114 due to the grating spacing and/orgrating orientation being different in the second intermediate-component815 than in the first intermediate-component 114.

In accordance with certain embodiments of the present technology, thesecond intermediate-component 815 is configured to cause the light thatis output from the optical waveguide 800 by the output-coupler 116 tohave a more uniform intensity distribution compared to if the secondintermediate-component 815 were absent and the light corresponding tothe image travelled by way of TIR from the first intermediate-component114 to the output-coupler 116 without interacting with the secondintermediate-component 815. More specifically, the secondintermediate-component 815 is configured to increase overlap of pupilsthat are replicated within the waveguide 800 compared to if the secondintermediate-component 815 were absent. This increase in pupil overlapcan be appreciated by comparing the replicated pupils (represented bydotted lined circles) in the waveguide 100 shown in FIG. 6B, where thereis no second intermediate-component, to the replicated pupils(represented by dotted lined circles) in the waveguide 800 shown in FIG.8A which includes the second intermediate-component 815.

The waveguide 800 is especially useful in a near-eye or heads-up displaysystem that includes a display engine (e.g., 204) configured to outputlight corresponding to an image, wherein the display engine includes anilluminator (e.g., 210) having one or more light sources each of whichis configured to emit narrowband light having a FWHM bandwidth that isless than 10 nm, e.g., as shown in and described above with reference toFIG. 4B. This is because, as described above with reference to FIGS. 5Band 6B, such narrowband light may result in small pupils that whenreplicated have gaps between adjacent replicated pupils, as representedin FIG. 6B, which gaps cause a non-uniform intensity distribution whenthe image is viewed from an eyebox proximate the output-coupler 116 ofthe optical waveguide 800. More specifically, if the secondintermediate-component 815 were not included within the opticalwaveguide 800, the narrowband light produced by the source(s) of theilluminator (e.g., 210) of the display engine (e.g., 204) would likelyresult in gaps between adjacent replicated pupils which would cause anon-uniform intensity distribution when the image is viewed from aneyebox proximate the output-coupler 116 of the optical waveguide 800.

In accordance with certain embodiments of the present technology, thesecond intermediate-component 815 diffracts and thereby interacts withthe light corresponding to the image travelled by way of TIR from thefirst intermediate-component 114 to the output-coupler 116. Preferably,the second intermediate-component 815 is configured to cause bothzero-order diffraction and at least one of positive or negativefirst-order diffraction. The zero-order diffractions caused by thesecond intermediate-component 815 results in a portion of the lightcorresponding to the image that is traveling from the first-intermediatecomponent 114 to the output-coupler 116 continuing in a same directionthat that light was traveling when it was incident on the secondintermediate-component 815. In other words, the zero-order diffractionscaused by the second intermediate-component 815 essentially result in aportion of the light traveling in the same manner that the portion ofthe light would if the second intermediate-component 815 was not there.On the other hand, the zero-order diffractions caused by the secondintermediate-component 815 results in a further portion of the lightcorresponding to the image that is traveling from the firstintermediate-component 114 to the output-coupler 116 to be diffracted ina new direction, e.g., sideways, which has an effect of increasing thesize of the pupils being replicated. Explain another way, by designingthe second intermediate-component 815 in a proper way, part of the powerof a pupil is deflected in a new direction into a diffractive order m,and the remaining part of the power of the pupil continues to propagatein its original direction. Then, with the next diffraction caused by thesecond intermediate-component 815, the diffracted power is re-diffractedand propagated at the original direction.

In accordance with certain embodiments of the present technology, thegrating equation m λ=d sin (sin θi±sin θr) is used to design the secondintermediate-component 815, where m is the diffractive order (e.g.,m=±0, 1, . . . k, where k is a small integer), λ is the wavelength oflight incident on the grating, d is the grating period, θi is the angleof incidence of light onto the grating, and θr is the angle at whichlight is reflected from the grating. More specifically, using thegrating equation, a diffraction direction is targeted to fill in gapsbetween adjacent pupils to obtain a more uniform pupil distribution.

As noted above, initially in the discussion of FIGS. 1A, 1B and 1C, incertain embodiments described herein one or more of the input-coupler112, the intermediate-component 114 (often referred to as the firstintermediate-component 114) and the output-coupler 116 can beimplemented as an SRG. Similarly, the second intermediate-component 815,and other DOEs described herein, can be implemented as SRGs. Such SRGscan all be located in or on the same one of the major planar surfaces(e.g., 108 or 110) of the bulk-substrate (e.g., 106) of an opticalwaveguide (e.g., 100). Referring, for example, to FIG. 8A, it is alsopossible that at least one of the input-coupler 112, the firstintermediate-component 114, the second intermediate-component 815 or theoutput-coupler 116 is an SRG formed in or on one of the major planarsurfaces (e.g., 108) of the bulk-substrate 106, while at least one otherone of the input-coupler 112, the first intermediate-component 114, thesecond intermediate-component 815 or the output-coupler 116 is an SRGformed in or on the other one of the major planar surfaces (e.g., 110)of the bulk-substrate 106.

In certain embodiments of the present technology, any one or more of aninput-coupler, an intermediate-component or an output-coupler can beimplemented as a double-sided SRG, or more generally, as a double-sidedDOE. For example, referring to FIG. 8B, which is an exemplary side viewof the waveguide 800 introduced with reference to FIG. 8A, the secondintermediate-component 815 is shown as being implemented as adouble-sided DOE that includes SRGs in both the major surfaces 108 and110 of the bulk substrate of the waveguide.

Where the second-intermediate component (e.g., 815) and/or some otheroptical element of a waveguide is implemented as a double-sided DOE, thegrating period and orientation of each DOE, of a pair of DOEs associatedwith the double-sided DOE, may be precisely matched so as to notadversely affect the modulation transfer function (MTF) of the imagingsystem and/or produce double imaging. For example, for the secondintermediate component 815, the grating period and orientation of theDOE included in or on the major surface 108 may be precisely matched to(i.e., the same as) the grating period and orientation of the DOEincluded in or on the other major surface 110.

One of the benefits of an intermediate-component (e.g., 815) beingimplemented as a double-side DOE is that it should provide for increasedpupil redistribution compared to if the intermediate-component were asingle-sided DOE. This is because a double-sided DOE will diffract andthereby interact with light corresponding to an image (travelled by wayof TIR within the waveguide) approximately twice as often as asingle-sided DOE. Beneficially, this could provide for even more imageuniformity than could be achieved if the second intermediate-component(e.g., 815) were implemented a single sided DOE.

Further, in accordance with certain embodiments of the presenttechnology, the number of intermediate-components may be greater thantwo in order to further improve the pupil redistribution, and thus,further improve image uniformity. The operational principles of theadditional intermediate-components (for example third and fourthintermediate-components) are the same as that of the second-intermediatecomponent 815 described with reference to FIGS. 8A and 8B. However, thegrating periods and grating orientation of the further (e.g., third andfourth intermediate-components) may be different than those of thesecond intermediate-component 815.

The high level flow diagram of FIG. 9 will now be used to summarizemethods according to various embodiments of the present technology. Suchmethods are for use with a display system that includes a display engineand an optical waveguide. Referring to FIG. 9, step 902 involves usingthe display engine (e.g., 204) to produce light corresponding to animage. Step 904 involves using an input-coupler (e.g., 112) of theoptical waveguide (e.g., 800) to couple the light corresponding to theimage into the optical waveguide and to direct the light correspondingto the image toward a first intermediate-component (e.g., 114) of theoptical waveguide. Step 906 involves using the firstintermediate-component (e.g., 114) of the optical waveguide (e.g., 800)to redirect the light corresponding to the image toward anoutput-coupler (e.g., 116) of the optical waveguide. Step 908 involvesusing a second intermediate-component (e.g., 815) of the opticalwaveguide (e.g., 800), which is a diffractive component located betweenthe first-intermediate component (114) and the output-coupler (116) ofthe optical waveguide, to perform pupil redistribution on a portion ofthe light corresponding to the image before the portion of the lightreaches the output-coupler. Step 910 involves using the output-coupler(e.g., 116) of the optical waveguide (e.g., 800) to couple, out of theoptical waveguide, the light corresponding to the image that hastraveled through the optical waveguide from the input-coupler (e.g.,112) to the output-coupler (e.g., 116) at least in part by way of totalinternal reflection (TIR).

In accordance with certain embodiments, step 906 can include using thefirst intermediate-component (e.g., 114) to perform one of horizontal orvertical pupil expansion on the light corresponding to the image that isdirected toward the first intermediate-component by the input-coupler,and step 910 can include using the output-coupler (e.g., 116) of theoptical waveguide to perform the other one of horizontal or verticalpupil expansion. For example, the first intermediate-component 114 canbe used to perform horizontal pupil expansion at step 906, and theoutput-coupler 116 can be used to perform vertical pupil expansion atstep 910. Alternatively, the first intermediate-component 114 can beused to perform vertical pupil expansion at step 906, and theoutput-coupler 116 can be used to perform horizontal pupil expansion atstep 910.

In accordance with certain embodiments, step 908 includes using thesecond intermediate-component 815 to cause the light that is output fromthe optical waveguide by the output-coupler 116 to have a more uniformintensity distribution compared to if the second intermediate-component815 were absent and the light corresponding to the image travelled byway of TIR from the first intermediate-component 114 to theoutput-coupler 116 without interacting with the secondintermediate-component 815. More particularly, step 908 can includeusing second intermediate-component 815 to increase overlap of pupilsthat are replicated within the waveguide 800 compared to if the secondintermediate-component 815 were not used.

In accordance with certain embodiments, step 906 includes using thefirst intermediate-component 815 to cause both zero-order diffractionand at least one of positive or negative first-order diffraction. Inaccordance with certain embodiments, step 908 can include using thesecond intermediate-component 815 to cause both zero-order diffractionand at least one of positive or negative first-order diffraction.

As was described above with reference to FIG. 2, a display engine 204can include an image former 206, an illuminator 210 and at least onecollimating lens 208. In accordance with certain embodiments of thepresent technology, step 902 involves using an illuminator (e.g., 210),which including one or more light sources, to emit (from each of thelight sources) narrowband light having a FWHM bandwidth that is lessthan 10 nm. In such embodiments, step 902 also includes using an imageformer (e.g., 206) to produce an image using the narrowband lightproduced by the illuminator (e.g., 210), and using at least onecollimating lens (e.g., 208) to collimate light corresponding to theimage produced by the image former and direct the light corresponding tothe image toward the input-coupler (e.g., 112) of the optical waveguide(e.g., 800). In accordance with certain such embodiments, step 908includes using the second-intermediate component (e.g., 815) to fill ingaps between adjacent replicated pupils and thereby increase pupiloverlap between adjacent replicated pupils associated with the lightcorresponding to the image and cause the light that is output from theoptical waveguide by the output-coupler to have a more uniform intensitydistribution compared to if the second intermediate-component (e.g.,815) were absent.

Were an optical waveguide includes an intermediate-component (e.g., 114)that used for pupil expansion, which is distinct from the input-coupler(e.g., 112) and output-coupler (116) of the waveguide (e.g., 100), theintermediate-component (e.g., 114) typically limits the diagonal FOV ofwaveguide based displays to no more than 35 degrees. In other words, anintermediate-component, e.g., 114, can typically only support a FOV upto about 35 degrees. By contrast, the input-coupler and theoutput-coupler of an optical waveguide are each able to support a muchlarger FOV than an individual intermediate-component. More specifically,the input-coupler and the output-coupler of an optical waveguide caneach support a FOV that is at least twice as large as an intermediatecomponent. Accordingly, the intermediate-component is typically theoptical component of an optical waveguide that limits the total FOV thatcan be achieved using the optical waveguide.

In order to increase the FOV that can be supported by an opticalwaveguide, an optical waveguide, such as the one shown in FIG. 10, maybe used. More specifically, referring to FIG. 10, the optical waveguide1000 is shown as including an input-coupler 1012, twointermediate-components 1014 a and 1014 b, and an output-coupler 1016.The input-coupler 1012 includes a diffraction grating and is configuredto couple light corresponding to an image associated with aninput-pupil, and having a corresponding FOV, into the optical waveguide1000 (and more specifically into the bulk-substrate of the opticalwaveguide). The input-coupler 1012 is also configured to diffract aportion of the light corresponding to the image in a first directiontoward the intermediate-component 1014 a such that a first portion ofthe FOV travels through the optical waveguide 1000 from theinput-coupler 1012 to the intermediate-component 1014 a, and diffract aportion of the light corresponding to the image in a second directiontoward the intermediate-component 1014 b such that a second portion ofthe FOV travels through the optical waveguide 1000 from theinput-coupler 1012 to the intermediate-component 1014 b. The first andsecond portions of the FOV differ from one another, and depending uponimplementation, may (or may not) partially overlap one another. Thefirst and second directions, in which the input-coupler 212 diffractslight, also differ from one another. In the configuration shown, thefirst direction is a leftward direction, and the second direction is arightward direction. More specifically, the first direction is bothleftward and acutely angled downward, and the second direction is bothrightward and acutely angled downward.

In the configuration shown, the intermediate-component 1014 a isconfigured to perform horizontal pupil expansion, and to diffract lightcorresponding to the first portion of the FOV, which travels through theoptical waveguide from the input-coupler 1012 to theintermediate-component 1014 a, toward the output coupler 1016. Theintermediate-component 1014 b is configured to perform horizontal pupilexpansion, and to diffract light corresponding to the second portion ofthe FOV, which travels through the optical waveguide from theinput-coupler 1012 to the intermediate-component 1014 b, toward theoutput coupler 1016. The intermediate-component 1014 a can also bereferred to more specifically as the left intermediate-component 1014 a,and the intermediate-component 1014 b can also be referred to morespecifically as the right intermediate-component 1014 b. Theintermediate-components 1014 a and 1014 b can individually be referredto as an intermediate-component 1014, or collectively asintermediate-components 1014. In alternative embodiments, the layout andoptical components can be rearranged and reconfigured (e.g., by rotatingthe layout by 90 degrees) such that the intermediate-components 1014 areconfigured to perform vertical pupil expansion, and the output-coupler1016 is configured to perform horizontal pupil expansion. Moregenerally, the intermediate-components can be configured to perform oneof horizontal or vertical pupil expansion, and the output-coupler can beconfigured to perform the other one of horizontal or vertical pupilexpansion.

In the configuration shown, the output-coupler 1016 is configured tocombine the light corresponding to the first and second portions of theFOV, which travel through the optical waveguide from theintermediate-components 1014 a and 1014 b to the output-coupler 1016.The output-coupler 1016 is also configured to couple the lightcorresponding to the combined first and second portions of the FOV outof the optical waveguide 1000 so that the light corresponding to theimage and the combined first and second portions of the FOV is outputfrom the optical waveguide 1000 and viewable from an output-pupil.

In a similar manner as was described above with reference to FIG. 6B,where pupils are relatively small (e.g., due to narrowband lightsource(s) being used to produce an image), pupils that are replicated bythe waveguide 100 may also be spread out such that they do not overlapone another, which detrimentally results in non-smooth pupil filling ofthe eyebox (proximate the output-coupler 1016) from which a human eyecan view the image. For example, the use of one or more LDs as the lightsource(s) of an illuminator can provide for a substantially uneven pupildistribution, which undesirably provides for a non-uniform intensitydistribution in the image. In a similar manner that thesecond-intermediate component 815 was added between the firstintermediate-component 114 and the output-coupler 116 in the discussionof FIG. 8A, one or more further intermediate-components can be added tothe waveguide 1000 introduced with reference to FIG. 10. This is shownin and discussed with reference to FIGS. 11 and 12.

Referring to FIG. 11, the optical waveguide 1100 shown therein issimilar to the optical waveguide 1000 described above with reference toFIG. 10, but two additional intermediate-components 1115 a and 1115 bare added. Referring to FIG. 12, the optical waveguide 1200 showntherein is similar to the optical waveguide 1000 described above withreference to FIG. 10, but one additional intermediate-components 1215 isadded. The added intermediate-components 1115 a and 1115 b in FIG. 11,and the added intermediate-component 1215 in FIG. 12, are configured tofunction in similar manners as the second intermediate-component 815described above with reference to FIG. 8A, namely, to perform pupilredistribution on respective portions of the light corresponding to animage before the portions of the light reach the output-coupler 1016.More specifically, these added intermediate-components cause the lightthat is output from the optical waveguide 1100 or 1200 by theoutput-coupler 1016 to have a more uniform intensity distributioncompared to if the added intermediate-component(s) were absent and thelight corresponding to the image travelled by way of TIR from theintermediate-component 1014 a and 1014 b to the output-coupler 1016without interacting with the added intermediate-component(s). Moregenerally, FIGS. 10-12 are used to illustrate how one or moreintermediate-components can be added to optical waveguides that havedifferent geometries than those discussed above with reference toearlier described FIGS. Further, it should be appreciated that thefunctionality of the second intermediate-component 815 described abovewith reference to FIG. 8A can be performed by more than one addedintermediate-component. For example, it would be possible to replace thesecond intermediate-component 815 in FIG. 8A and its functionality witha left second intermediate-component and a right secondintermediate-component.

Embodiments of the present technology, which are described above, can beused to provide for a more uniform pupil distribution, and therebyprovide for a more uniform image. Preferably, embodiments of the presenttechnology, which are described above, cause the light that is outputfrom a waveguide by an output-coupler to have a more uniform intensitydistribution, so that any non-uniformity in intensity is imperceptibleto a human eye viewing an image using the waveguide. A substantiallyuniform angular intensity distribution is especially beneficial inapplications where the location of a user's eye(s) is/are fixed relativeto the waveguide(s), e.g., in a head-mounted-display (HMD) or othernear-eye-display (NED) application. An overall goal of having the light,output by the waveguide, having a substantially uniform intensitydistribution is so that any non-uniformity in intensity is imperceptibleto a human eye viewing an image using the waveguide.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. An apparatus for use in replicating an imageassociated with an input-pupil to an output-pupil, the apparatuscomprising: an optical waveguide including an input-coupler, a firstintermediate-component, a second intermediate-component and anoutput-coupler; the input-coupler of the optical waveguide configured tocouple, into the optical waveguide, light corresponding to the imageassociated with the input-pupil and configured to direct the lightcorresponding to the image toward the first intermediate-component; thefirst intermediate-component configured to perform one of horizontal orvertical pupil expansion on the light corresponding to the image that isdirected toward the first intermediate-component by the input-couplerand configured to redirect the light corresponding to the image towardthe output-coupler; the second intermediate-component being adiffractive component located between the first-intermediate componentand the output-coupler and configured to perform pupil redistribution ona portion of the light corresponding to the image before the portion ofthe light reaches the output-coupler; and the output-coupler configuredto perform the other one of horizontal or vertical pupil expansion andconfigured to couple, out of the optical waveguide, the lightcorresponding to the image that has traveled through the opticalwaveguide from the input-coupler to the output-coupler at least in partby way of total internal reflection (TIR).
 2. The apparatus of claim 1,wherein the second intermediate-component diffracts and therebyinteracts with the light corresponding to the image travelled by way ofTIR from the first intermediate-component to the output-coupler.
 3. Theapparatus of claim 2, wherein the first intermediate-component isconfigured to cause both zero-order diffraction and at least one ofpositive or negative first-order diffraction, and wherein the secondintermediate-component is configured to cause both zero-orderdiffraction and at least one of positive or negative first-orderdiffraction.
 4. The apparatus of claim 2, wherein: the optical waveguideincludes a first major surface and a second major surface opposite thefirst major surface; and the second intermediate-component comprises adouble-sided DOE including a first grating that is formed in or on thefirst major surface and a corresponding second grating that is formed inor on the second major surface; and each of the first and secondgratings of the double-side DOE diffract and thereby interact with thelight corresponding to the image travelled by way of TIR from the firstintermediate-component to the output-coupler.
 5. The apparatus of claim2, wherein the second intermediate-component is configured to cause thelight that is output from the optical waveguide by the output-coupler tohave a more uniform intensity distribution compared to if the secondintermediate-component were absent and the light corresponding to theimage travelled by way of TIR from the first intermediate-component tothe output-coupler without interacting with the secondintermediate-component.
 6. The apparatus of claim 1, wherein the secondintermediate-component is configured to increase overlap of pupils thatare replicated within the waveguide compared to if the secondintermediate-component were absent.
 7. The apparatus of claim 1, whereinwith respect to a front view of the waveguide: the firstintermediate-component is located to a side of the input-coupler; thesecond intermediate-component is located below the firstintermediate-component; and the output-coupler is located below thesecond intermediate-component.
 8. A method use with a display systemthat includes a display engine and an optical waveguide, the methodcomprising: using the display engine to produce light corresponding toan image; using an input-coupler of the optical waveguide to couple thelight corresponding to the image into the optical waveguide and todirect the light corresponding to the image toward a firstintermediate-component of the optical waveguide; using the firstintermediate-component of the optical waveguide to redirect the lightcorresponding to the image toward an output-coupler of the opticalwaveguide; using a second intermediate-component of the opticalwaveguide, which is a diffractive component located between thefirst-intermediate component and the output-coupler of the opticalwaveguide, to perform pupil redistribution on a portion of the lightcorresponding to the image before the portion of the light reaches theoutput-coupler; and using the output-coupler of the optical waveguide tocouple, out of the optical waveguide, the light corresponding to theimage that has traveled through the optical waveguide from theinput-coupler to the output-coupler at least in part by way of totalinternal reflection (TIR).
 9. The method of claim 8, wherein: the usingthe first intermediate-component includes using the firstintermediate-component to perform one of horizontal or vertical pupilexpansion on the light corresponding to the image that is directedtoward the first intermediate-component by the input-coupler; and theusing the output-coupler includes using the output-coupler of theoptical waveguide to perform the other one of horizontal or verticalpupil expansion.
 10. The method of claim 8, wherein the using the secondintermediate-component causes the light that is output from the opticalwaveguide by the output-coupler to have a more uniform intensitydistribution compared to if the second intermediate-component were notused and the light corresponding to the image travelled by way of TIRfrom the first intermediate-component to the output-coupler withoutinteracting with the second intermediate-component.
 11. The method ofclaim 8, wherein the using second intermediate-component increasesoverlap of pupils that are replicated within the waveguide compared toif the second intermediate-component were not used.
 12. The method ofclaim 8, wherein the using the first intermediate-component includesusing the first intermediate-component to cause both zero-orderdiffraction and at least one of positive or negative first-orderdiffraction.
 13. The method of claim 12, wherein the using the secondintermediate-component includes using the second intermediate-componentto cause both zero-order diffraction and at least one of positive ornegative first-order diffraction.
 14. The method of claim 8, wherein theusing the display engine to produce light corresponding to an imageincludes: using an illuminator including one or more light sources toemit, from each of the light sources, narrowband light having a fullwidth at half maximum (FWHM) bandwidth that is less than 10 nm; using animage former to produce an image using the narrowband light produced bythe illuminator; and using at least one collimating lens to collimatelight corresponding to the image produced by the image former and directthe light corresponding to the image toward the input-coupler of theoptical waveguide.
 15. The method of claim 14, wherein the using thesecond-intermediate component includes using the second-intermediatecomponent to fill in gaps between adjacent replicated pupils and tothereby increase pupil overlap between adjacent replicated pupilsassociated with the light corresponding to the image and cause the lightthat is output from the optical waveguide by the output-coupler to havea more uniform intensity distribution compared to if the secondintermediate-component were not used.
 16. A near-eye or heads-up displaysystem, comprising: a display engine configured to output lightcorresponding to an image; an optical waveguide including aninput-coupler, a first intermediate-component, a secondintermediate-component and an output-coupler; the input-coupler of theoptical waveguide configured to couple, into the optical waveguide,light corresponding to an image produced by the display engine andconfigured to direct the light corresponding to the image toward thefirst intermediate-component of the optical waveguide; the firstintermediate-component of the optical waveguide configured to redirectthe light corresponding to the image toward the output-coupler; thesecond intermediate-component being a diffractive component locatedbetween the first-intermediate component and the output-coupler andconfigured to perform pupil redistribution on a portion of the lightcorresponding to the image before the portion of the light reaches theoutput-coupler; and the output-coupler configured to couple, out of theoptical waveguide, light corresponding to the image that has traveledthrough the optical waveguide from the input-coupler to theoutput-coupler at least in part by way of total internal reflection(TIR).
 17. The system of claim 16, wherein: the firstintermediate-component of the optical waveguide is configured to performone of horizontal or vertical pupil expansion on the light correspondingto the image that is directed toward the first intermediate-component bythe input-coupler; and the output-coupler of the optical waveguide isconfigured to perform the other one of horizontal or vertical pupilexpansion.
 18. The system of claim 16, wherein the display engineincludes: an illuminator including one or more light sources each ofwhich is configured to emit narrowband light having a full width at halfmaximum (FWHM) bandwidth that is less than 10 nm; an image formerconfigured to produce an image using the narrowband light produced bythe illuminator; and at least one collimating lens arranged andconfigured to receive and collimate light corresponding to the imageproduced by the image former and direct the light corresponding to theimage toward the input-coupler of the optical waveguide.
 19. The systemof claim 18, wherein if the second intermediate-component of the opticalwaveguide were not included within the optical waveguide, the narrowbandlight produced by the one or more light sources of the illuminator ofthe display engine would result in gaps between adjacent replicatedpupils which would cause a non-uniform intensity distribution when theimage is viewed from an eyebox proximate the output-coupler of theoptical waveguide.
 20. The system of claim 15, wherein: the secondintermediate-component diffracts and thereby interacts with the lightcorresponding to the image travelled by way of TIR from the firstintermediate-component to the output-coupler; and the secondintermediate-component is configured to cause both zero-orderdiffraction and at least one of positive or negative first-orderdiffraction.